The present invention relates to the field of medical devices and more particularly to embolization coils.
The present invention relates to an assembly for positioning an embolization coil in the vascular system, comprising a delivery wire having a distal section with a central core and a threading coil fixed to the central core.
An assembly of this kind is known from U.S. Pat. No. 5,725,534 in which the threading coil is fixed on a cylindrical distal end portion of a guidewire core member. The distal end portion has a diameter corresponding to the inner diameter of the threading coil. Due to the relatively large diameter of the core, the core can have a relatively high rigidity which renders it difficult to advance the embolization coil to deployment sites in very narrow blood vessels that require access via tortuous paths.
A number of other methods for controlled release of embolization coils are known. WO 93/11823 describes an assembly in which the core at its distal end has two axially spaced soldered-on radial enlargements that lock coil ends to the core. In both WO 93/11825 and U.S. Pat. No. 5,250,071 a releasable geometrical locking is used between the coil and the guidewire, and in U.S. Pat. No. 5,122,136 the coil is affixed to the guidewire at thin connecting areas which are electrolytically eroded away when the coil is positioned at the desired site.
The object of the present invention is to provide an assembly that can access small and remote vascular sites more easily for easy and secure placement of the embolization coil.
The assembly of the present invention is accordingly designed with a delivery wire having a distal section with a central core and a threading coil, the central core including a blade-shaped portion having a blade thickness measured between sides and a blade width measured between edges, the threading coil having turns arranged with a pitch and affixed to the central core at least at the edges of the blade-shaped portion, and the blade thickness being less than the blade width, such as between 10% and 60% and preferably being 40% or less thereof.
The blade-shaped portion carrying the threading coil is much more flexible and easy to bend in the thickness direction of the blade than in the direction of the width where the blade dimension is the largest. The blade-shaped portion is a distal end portion of the central core, and if it is subjected to a torque, the central core twists. When the delivery wire is advanced through a catheter and has to pass through a curvature, the bladeshaped portion touches the inner wall of the catheter and is subjected to a torque until the blade-shaped portion itself has turned with the direction of width transverse to the curvature. The result is that the bending occurs in the thickness direction which is most flexible. Fixation of the threading coil at the edges provides control of the positioning of the threads so that the un-threading of the embolization coil occurs very smoothly. This is especially so in cases where the coil is positioned at the delivery site in an oblique position with respect to the threading coil, which could have caused increased friction had the threaded coil been fixed on a cylindrical member.
In one embodiment, the blade width is less than the inner diameter of the threading coil, and this reduces the bending rigidity of the blade-shaped portion.
In another embodiment the edges of the blade-shaped portion are provided with recesses in which the turns of the threading coil are seated. These recesses can for example be laser-cut or etched into the blade-shaped portion. They provide a high security for locking of the threading coil, even if it is not fixed by other means than the geometrical interlocking of recesses and coil turns.
In embodiments where the threading coil is fixed by use of solder, the solder is positioned on at least one of the flat sides of the blade-shaped portion in a wave-shaped pattern, with the threading coil located on the wave crests and with the bottom of the wave troughs located less than a distance d from the flat side, where the distance d is at most xc2xc of the inner diameter D of the threading coil. Even though the solder is a soft material without great resistance to bending, it is favorable to minimize the presence of the material so that the relatively high bending flexibility is retained in the direction of thickness of the blade-shaped portion. Extending the very deep wave troughs to positions close to the blade-shaped portion allows mutual flexure of the wave crests when the blade-shaped portion bends.
Preferably, the distal end of the threading coil terminates at a position less than twice the diameter of the threading coil wire from one of the flat sides of the blade-shaped portion. The threading coil wire has very diminutive dimensions and any permanent bending of its distal end can be detrimental to the functioning of the thread. By using a microscope it is possible to adjust the threading coil wire to terminate close to the flat side of the blade-shaped portion to which it is fixed. It is also an advantage that there is no lengthy, protruding threading coil wire end that could cause harm to vascular tissue.
The threading coil or the blade-shaped portion can be made of radiopaque material in order to be discerned on an image screen by the radiologist or neuroradiologist that introduces the detachable coil into the vascular system of a patient, but in order to be seen clearly it ought to have relatively large dimensions. The blade-shaped portion can be difficult to see if the image shows it in a sideview. This drawback of making the central core blade-shaped can be made up for by positioning a radiopaque marker at a predefined first distance, such as about 3 to 3.5 cm, proximal to the distal termination of the threading coil. In this embodiment it is not required for the threading coil or the blade-shaped member to be radiopaque, because the marker indicates the position from the first distance.
In a further development of the latter embodiment, the assembly includes a catheter having a distal delivery opening, with a radiopaque marker at a predetermined second distance proximal to the delivery opening; and the first distance on the delivery wire and the second distance on the catheter are such, that the distal termination of the threading coil is positioned at the delivery opening when the marker on the delivery wire is positioned at the marker on the catheter. By also including a marker on the catheter, the requirement for judging distances on a screen can to a large extent be dispensed with. In order to obtain correct positioning of the threading coil at the delivery opening all that is required is to advance the delivery wire until the marking on the wire is observed on the screen, to attain the predefined position relative to the marker on the catheter. If the markers have a short length, the predefined position can be one of mutual overlap; but in case the markers are longer, in order to be clearly visible it is preferred that the predefined position is attained when the distal edge of the marker on the delivery wire has been advanced exactly to the proximal edge of the marker on the catheter.
The security of the placement can be further improved by an embodiment in which a pin vise has fixing means for detachable fixing on the delivery wire and carries a cannula of a length of at least 8 cm through which the delivery wire is insertable. This pin vise can be placed at the proximal end of the catheter system prior to inserting the delivery wire. The length of the cannula ensures that it can extend through a Y-connector and a fitting mounted on the proximal end of the catheter. The distal end of the cannula is positioned in the catheter. When the delivery wire is inserted through the pin vise, fluid will flow out through the cannula outside the patient and clean the embolization coil and the delivery wire while these are introduced.
The present invention furthermore relates to a method of introducing a detachable embolization coil into a deployment site in the vascular system. According to the method of the present invention: a catheter system with a catheter having a radiopaque marker is positioned in the vascular system with its distal delivery opening at the deployment site and with the proximal end of the catheter system outside the patient; a delivery wire is advanced through the catheter until a radiopaque marker on the delivery wire is positioned at a radiopaque marker on the catheter; a pin vise is then positionally locked on the delivery wire in abutment against the proximal end of the catheter system; then, the pin vise is rotated in a detach direction until the embolization coil is detached from the delivery wire.
The method is safe to use because it assures in a convenient manner that the distal termination of the delivery wire is exactly at the delivery opening or on the proximal side thereof when the embolization coil is detached, so that on one hand the threading coil is unable to damage the vascular wall, and on the other hand the detached coil gets completely clear of the catheter and cannot be inadvertently pulled away from the deployment site when the delivery wire and the catheter are retracted from the vascular system.